In practice conveyor belts are used for conveying a viscous mix such as a bituminous or concrete mix or also sand or gravel. For road finishers or chargers conveyor belts are particularly useful for transporting the mix from a material bunker to a screed. Conveyor belts, which are installed in chargers or road finishers, are difficult to access which in turn leads to high maintenance costs. In addition the conveyor belts must be regularly checked before starting work to ensure that sufficient conveyor belt tension is available or that the belt runs in the appropriate direction so that no damage to the conveyor belt system can occur.
Known conveyor systems are mechanically tensioned by a threaded spindle. A threaded spindle can be fitted to the right and left near the driving drum, whereby the setting of the threaded spindle is set manually before the conveyor system starts up. A manual adjustment method of this nature can also influence the running of the belt. If it is found during the work, that the belt run has changed, a manual readjustment has to be made on the threaded spindle. In addition, one problem is that the road finisher or charger must be stopped, because correction during operation is not possible. Often it may happen that incorrect running of the conveyor belt is not noticed quickly enough. Then it may be that the conveyor belt runs out of true over the guide rollers and then rubs on the conveyor belt frame. With incorrect running of this nature, in which the conveyor belt rubs on the frame, damage to the belt may result. Similarly, the manual setting of the threaded spindle requires a certain routine which may be different depending on the person who makes the adjustment.
DE 697 06 861 T2 describes a mechanical conveyor-track guide arrangement for controlling the running of conveyor belts. The belt-steering arrangement consists of a steering bearer with two steering rollers to guide a conveyor belt when it runs in its transport direction. Here, the steering bearer can rotate or swivel about a first point of rotation which is located on a beam or girder. In addition the belt steering arrangement consists of a guide bearer with guide rollers which are arranged to abut on each of the outer sides of the belt. In this way a sideward displacement of the conveyor belt can be prevented. A disadvantage here is that with contact with the guide rollers a certain frictional wear arises on the conveyor belt and due to the increased running resistance a higher drive energy is required.
US 2003/0045966 A1 relates to a moving belt arrangement for the automatic centring of the conveyor belt. Here, the run of the belt is monitored by means of sensors, whereby an unwanted running direction can be detected in order to change the setting of a drive roller such that the running belt runs back to its original position. To check the running of the belt a magnetic element is integrated into the belt which is monitored by a sensor arrangement. However, conveyor belts in road construction are subjected to high thermal stresses and must withstand high tensile stresses due to the heavy mix to be transported. Therefore it is extremely questionable whether a running belt arrangement as described by US 2003/0045966 A1 is suitable for application in road construction.
DE 202 10 624 U1 describes a tensioning device for conveyor belts. Here, a drive roller is tensioned at both ends by two hydraulic cylinders. The tension of the conveyor belt can be monitored by means of sensors, whereby the hydraulic tensioning system is activated when the tension is insufficient. Here, firstly a differential cylinder is subjected to pressure, which simultaneously propagates to the second differential cylinder through a pressure line, whereby simultaneous displacement occurs at both ends of the drive roller to evenly tension the belt.